An Intriguing Pattern of Rotating Spirals Made By Falling Liquid

Researchers report an interesting observation of anti-spirals in a nonoscillatory medium.

It’s a new example of rotating spiral patterns formed spontaneously in a liquid system.

The formation of patterns in nonequilibrium systems has attracted a lot of attention in many technical fields, as knowing self-organization processes could provide valuable insights into their complex behavior. Numerous studies, in particular, have focused on spiral patterns that emerge through chiral symmetry breaking.

Galaxies and cyclones are some of the well-known examples of spiral patterns in nature. When they revolve, spirals spin with their arms trailing the rotational direction. Some spirals (called anti-spirals) can also spin in the opposite direction of rotation. However, such events are quite rare.

Recently, researchers at Hokkaido University (Japan) and the University of Côte d’Azur (France) reported an interesting observation of spontaneous anti-spirals in a nonoscillatory medium. They observed the pattern at a downward-facing free surface of a horizontal liquid film.

Experimental Setup

The team used a cylindrical reservoir with several small holes at its bottom, and filled it with silicone oil. The oil falls through the holes at a certain rate, creating a thin layer beneath the reservoir.

When this layer attains a specific thickness, it becomes unstable to liquid discharges falling from the layer’s downward-facing surface in the form of curtains, columns, or droplets. In this study, the team fine-tuned the liquid supply rate in such a way that it formed curtains while falling from the reservoir’s holes.

They used a phenomenologically constructed cellular automaton to demonstrate that such unique patterns evolve from the phase locking leading to periodic fluid discharge at a particular flow rate over the entire surface (downward-facing) of the layer.

Courtesy of researchers

The liquid curtains slowly wind around the core region, transforming into well-balanced spirals with up to 6 arms that rotated either clockwise or anticlockwise. What researchers saw, in this case, were anti-spirals rotating inwards.

The destabilization of the layer beneath the reservoir occurs due to a phenomenon called Rayleigh-Taylor instability. This creates antispiral patterns in the form of propagating oil curtains.

What’s Next?

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The formation of different types of spirals has been extensively studied in oscillatory media. This present work describes a new example of rotating spiral patterns formed spontaneously in a liquid system that must be externally controlled to create periodic structures.